Photocatalytic Degradation Of Phenol By Rutile Titanium Dioxide Nanoarrays

As a photocatalyst,TiO₂ has the advantages of low cost,strong oxidation capability,environmental benign and so on.Nanorods arrays make full use of in-depth space and in turn provide more photocatalytic active sites in limited spaces.Single crystallites avoid the scattering effect arising from grains,which enhances the charge separation and transportation rates.Single-crystalline rutile TiO₂ nanorod arrays are thus good candidates for photoelectrochemical（PEC）degradations of phenol in water,which exhibit a high quantum efficiency.A mixture of aqueous tetrabutyltitanate（TBT）and HCl solution was used to precipitate single-crystalline rutile TiO₂ nanorod arrays on metallic Ti substrates under a hydrothermal environment.The achieved array exhibits high efficiency towards PEC degradations of phenol in water.Hydrothermal time is an important parameter for the growth of rutile nanorods.Fully developed TiO₂ nanorod arrays could be seen clearly beyond 3 h.The smaller nanorods could be fused with each other to form larger nanorods upon prolonged durations via an oriented attachment mechanism.The amount of TBT determined the density of rutile nanorods,which reduced with decreasing TBT in the reactant.When the TBT amount was further reduced to be less than a critical value,the titanium substrates would be dissolved thoroughly by the erosion of HCl.The nanorod arrays prepared herein are single crystal rutile TiO₂ with a band gap of 2.85 eV.The PEC evaluation reveals that,the reaction rate increased with increasing hydrothermal time because of more loaded TiO₂.The maximum reaction rate constant was 2.74 h^-1,which was 39 times that of commercial P25 TiO₂nanoparticulate film.The photocurrent stabilized at 0.9 mA cm^-2 under the illumination of AM1.5G simulated solar light,suggesting a high separation efficiency of photogenerated holes and electrons.The pH value and anions in the phenol solution affect readily the PEC efficiency:an acidic environment greatly promotes the phenol degradation;whilst phosphate and fluorine ions hindered the PEC degradation reaction under the acidic environment.TiO₂ nanotree arrays were successfully synthesized using a wet precipitation approach to grow branches on the rutile TiO₂ nanorod arrays.As the deposition time increased,the number of nano-branches increased,and the original small branches grew up.Hydrogen peroxide in the precursor etched the nanorod trunk.The nanotree as a whole is rutile TiO₂ and the band gap reduced slightly to 2.74 eV.The photocurrent of rutile nanorod and nanotree photoanodes was 0.68 mA cm^-2 and 0.30mA cm^-2 under simulated solar light,respectively,which suggests that the branching procedure produces deficiencies unfavorable for the photocurrent production.In the test of PEC degradation of phenol,the reaction rate constants of TiO₂ nanotrees with branch-growing time of 8 h,16 h and 24 h are 0.97 h^-1,2.07 h^-1 and 0.61 h^-1,respectively;whilst that of the pristine TiO₂ nanorods is 0.77 h^-1.The phenol degradation efficiency of TiO₂ nanotrees with a branch-growing time less than 16 h was higher than that of TiO₂ nanorods,which can be contributed to the increased specific surface area providing more active sites.In the process of phenol degradation,the photocurrent of rutile nanotrees was larger than that of nanorods.